Metal-cutting saw bow frame including a device for tensioning of the blade

ABSTRACT

The frame of a metal-cutting saw of the one-piece, hacksaw type includes a bow (6) extended at its rear end by a pistol grip (3) and a protective branch (7) and at its front end by a branch (9) which at its end includes an attachment stud (14) for receiving one of the two ends of a blade (2). The pistol grip (3) has a blade-tensioning device comprised of a blade-tension adjustment system (4) including a lever fixed by an articulation pin (18) to an articulation stirrup piece (8) which extends into the rear part of the protective branch (7). The articulation pin (18) constitutes an axis about which the lever (5) can rotate. The blade-tension adjustment system (4) further includes a blade support (12) which receives the other end of the blade (2) and an opening (12a) for allowing the articulation pin (18) to pass through. A threaded rod (15) is connected to the blade support (12), and provides for articulation of the lever (5) about an articulation pin (17). The articulation pin (17) has a smooth hole for receiving the threaded rod (15), and receives an adjustable thumbwheel (16) which bears against the articulation pin (17).

BACKGROUND OF THE INVENTION

The present invention generally relates to a frame for a metal-cuttingsaw of the one-piece hacksaw type including a bow extended at its rearend by a pistol grip. The pistol grip includes a hand-protection branchwhich meets the grip at the lower part, and which incorporates ablade-tensioning mechanism.

The user of a metal-cutting saw needs to change the blade of his tooleither regularly, because the blade is becoming worn, or to change thetype of blade depending on the specific type of cutting being done. Allof these blade changes tend to make the blade tensioning increasinglyless precise.

Metal-cutting saws having adjustable blade-tensioning devices havepreviously been proposed in order to solve this problem. For example,French Patent Application No. 2,624,780 discloses a device having aprofiled lever with a cam shape which is capable of pushing up againstand then tilting against the opposing face of the blade-holder arm. Thelever is associated, via its lower part, with the outer end of atension-retaining member, or fitting. The fitting allows the tension tobe adjusted by altering the position of a nut provided on the fitting.

The disclosed device, which is relatively quick to operate, does notallow the blade to be adjusted very accurately because the position ofthe nut provided for achieving such adjustment can vary only by wholenumbers of turns.

U.S. Pat. Nos. 4,367,779 and 4,466,471 also disclose metal-cutting sawswith mechanisms for adjusting the tension of the blade using a lever inthe hand grip of the saw which pivots to create tension in the bladethrough a rod which acts on a lever arm. In each case, the tension isadjusted by varying the length of the rod.

Although generally satisfactory, such devices are on the one handcomplicated to operate, while on the other hand, because of theirsignificant number of component parts, such devices are not very robustfrom a mechanical point of view.

Accordingly, it is an object of the present invention to overcome thedrawbacks of these prior devices while allowing the user to preset thetension in the saw blade.

Another object of the present invention is to allow the blade to befitted quickly, by limiting the number of operations to be carried outon the frame.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects areachieved by providing the frame of a metal-cutting saw of the one-piecehacksaw type with a bow which is extended at its rear end by a pistolgrip having a protective branch, and which is extended at its front endby a branch which, at its end, includes an attachment stud for receivingone of the two ends of a blade. The attachment stud includes ablade-tensioning device which comprises a blade-tension adjustmentsystem having a lever fixed by an articulation pin to an articulationstirrup piece which extends into the rear part of the protective branch.The articulation pin constitutes an axis about which the lever canrotate. The blade-tension adjustment system comprises a blade supportwhich receives the other end of the blade and which includes an openingallowing the articulation pin to pass through, and a threaded rod whichis on the one hand permanently connected to the blade support and whichis on the other hand articulated to the lever by an articulation pin.The articulation pin is provided with a smooth hole through which thethreaded rod can pass. A thumbwheel is screwed onto the thumbwheel, andbears against the pierced articulation pin.

The saw frame preferably includes, in combination, a hand grip, a rearbranch of the bow and a stirrup piece for articulating the lever. Alower part of the grip has a shape which mates with the lever andprotects the tension-adjustment members, and mates with the bow, whichhas a changing cross-section that curves toward the blade. Also providedis an ergonomically designed region on which the operator's thumb canrest and which is positioned on the upper branch of the bow, a regionagainst which the blade can rest and a stub that holds the blade at thelower end of the front branch of the bow.

The present invention will be better understood with reference to thedescription which is provided below, together the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the saw frame of the present invention, withthe blade-tensioning system in the closed position and with the lowerpart of the hand grip incorporating the adjustment system being cut awayto show internal structures.

FIG. 2 is a view similar to FIG. 1, but with the blade-tensioning systemin the open position.

FIG. 3 is an exploded view of the adjustment members.

FIG. 4 is a perspective view of the blade support.

FIG. 5a is a top view of the blade-tensioning lever.

FIG. 5b is a cross-sectional view, taken along the line BB, of the leverof FIG. 5a.

FIG. 6 is a cross-sectional view, taken along the line AA, of the bow ofFIG. 1.

FIGS. 7a and 7b are side views of the blade-tension adjustment systemfor achieving different blade tension settings.

FIG. 8 is a side view of the front part of the bow during positioning ofthe blade.

FIG. 9 is a side view of the metal strip associated with the bow.

FIG. 10 is a side view, in longitudinal cross-section, of the saw frameof the present invention, illustrating the position of the metal stripshown in FIG. 9.

FIG. 11 is a cross-sectional view, taken along the line AA, of the bowshown in FIG. 10.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1 to 11 show the frame of a metal-cutting saw (1) which, in theembodiment shown, is of the hacksaw type. The saw (1) comprises a bow(6) extended at its rear end by a pistol grip (3) and a protectivebranch (7) for protecting the user's hand. The lower part of the pistolgrip (3) incorporates a tension-adjustment system (4).

The blade (2) is fixed at both of its ends. One end is fixed to the endof a branch (9) which has an attachment stud (14). The other end isfixed to a blade support (12) which includes an attachment stud (13).The blade support (12) constitutes one of the elements of thetension-adjustment system (4).

A lower extension of the protective branch (7) has an articulationstirrup piece (8) which includes a hole for receiving an articulationpin (18). The articulation pin (18) receives a lever (5), andconstitutes a pin about which the lever (5) can rotate. The lower partof the pistol grip (3), which is situated between the rear of thearticulation stirrup piece and the lever (5), has a shape that mateswith the adjustment system for receiving the blade-tension adjustmentsystem when the lever (5) is in its closed and self-locking position.

The blade support (12) has an opening (12a). The articulation pin (18)passes through the opening (12a) for movement in a direction more orless perpendicular to the longitudinal axis of the blade. The opening(12a) may be oblong, and preferably has more or less the shape of aright-angled trapezium with rounded corners. The lever (5) can pivotabout the articulation pin between a closed position (as shown in FIGS.1, 7a and 7b) and an open position (as shown in FIG. 2).

A hole (12b) is provided in the wall of the blade support (12) so thatone of the ends of a threaded rod (15) can be screwed into the bladesupport. The threaded rod (15) also passes, with clearance, through asmooth hole drilled in an articulation pin (17). A thumbwheel (16) isscrewed onto the other end of the threaded rod (15) so as to control thetravel of the articulation pin (17). In its preferred embodiment, thethreaded rod (15) has a smooth section (15a) to better allow the piercedarticulation pin (17) to slide.

A slot (5a) is provided in the lever (5) to receive the articulation pin(17) for secured articulation relative to the threaded rod (15), andindirectly, to the blade support (12), making it possible for thearticulation pin (17) to slide in the slot (5a).

Collectively, the blade support (12), the threaded rod (15), the piercedarticulation pin (17) and the thumbwheel (16) make up the blade-tensionadjustment system.

Advantageously, the end of the branch (9) has a retaining stub (11) withan inclined side (11a) facing toward the outside of the bow, above theattachment stud (14). As illustrated in FIG. 8, the blade (2) ispositioned parallel to the inclined side (11a) of the stub (11) so thatone of its ends can be fitted over the attachment stud (14). The bladeis pivoted counter-clockwise so that its other end can be slipped overthe attachment stud (13) of the blade support.

When the lever (5) is in the open position, the blade support is given acertain amount of latitude for movement in the mid-plane of the frame.The tension is adjusted by turning the thumbwheel (16) on the threadedrod (15). In this way, the thumbwheel (16) is caused to bear on andreact against the pierced articulation pin (17).

The blade is tensioned by the force exerted by the user on the lever (5)so as to bring the lever (5) back into the closed position, passingthrough a point of equilibrium in which the points A, B and C, therespective centers of the attachment stud (14), the attachment pin (18)and the articulation pin (17), are aligned. The lever (5) is then in aself-locking position, with the point C being above a straight line thatpasses through the points A and B.

The difference in distances (20a)-(20b) corresponding to the travel ofthe point C generates tension in the blade (2) by `elastic` deformationof the bow (6). To withstand these deformation forces, the bow has anI-shaped cross-section (7a). Preferably, this I-shaped cross-section islocally ribbed in a horizontal section (7b) passing through thehorizontal mid-plane of the I-shaped cross-section, as illustrated inFIG. 6. This section changes and is curved toward the blade. To furtherimprove the resistance to these deformation forces, a metal strip (7c)having a rectangular cross-section (e.g., having an I-shapedcross-section) is inserted inside the bow. The strip (7c) extends moreor less as far as the end of the branch (9) where the attachment stud(14) is situated. In this way, the L-shaped metal insert operates toensure that the bow will be rigid and that the attachment stud or stubis held at its front end.

For optimum comfort in use, the front face of the branch (9) has anergonomic resting region (10), and the upper branch of the bow has aregion (10a) for positioning the user's thumb.

What is claimed is:
 1. A frame for a metal-cutting saw comprising:a bow,wherein the bow is extended at a rear end by a pistol grip and aprotective branch, and wherein the bow is extended at a front end by abranch having an end which includes an attachment stud for receiving afirst end of a blade; and a blade-tensioning device having ablade-tension adjustment assembly, wherein the blade-tensioning deviceincludes a lever fixed by a first articulation pin to an articulationstirrup piece which extends into a rear part of the protective branch,wherein the first articulation pin defines an axis about which the levercan rotate, and wherein the blade-tension adjustment assembly includes ablade support for receiving a second end of the blade, an opening forreceiving the first articulation pin therein, a threaded rod connectedto the blade support and connected for articulation relative to thelever by a second articulation pin which includes a hole for receivingthe threaded rod, and a thumbwheel threadingly engaging the threaded rodand bearing against the second articulation pin.
 2. The frame of claim 1wherein the metal-cutting saw is a one-piece hacksaw.
 3. The frame ofclaim 1 wherein a lower part of the pistol grip is located between therear of the articulation stirrup piece and the lever.
 4. The frame ofclaim 3 wherein the lower part of the pistol grip has a shape that mateswith the blade-tension adjustment assembly, for receiving theblade-tension adjustment assembly when the lever is in a closed andself-locking position.
 5. The frame of claim 1 wherein the opening has ashape which approximates a trapezium with rounded corners.
 6. The frameof claim 1 wherein the first articulation pin slidingly passes throughthe opening, for movement in a direction which is substantiallyperpendicular to a longitudinal axis defined by the blade.
 7. The frameof claim 1 wherein the lever includes a slot for receiving the secondarticulation pin, for securing the second articulation pin to thethreaded rod for articulation relative to the threaded rod.
 8. The frameof claim 1 wherein the threaded rod has a smooth section for freely andslidingly receiving the second articulation pin.
 9. The frame of claim 1wherein the end of the branch has a retaining stub located above theattachment stud.
 10. The frame of claim 9 wherein the retaining stub hasan inclined side facing toward outside portions of the bow.
 11. Theframe of claim 1 which further includes a metal strip located inside thebow, wherein the metal strip extends approximately to the end of thebranch, to a position substantially adjacent to the attachment stud. 12.The frame of claim 11 wherein the metal strip has a substantiallyrectangular cross-section.
 13. The frame of claim 1 wherein the bow hasa substantially I-shaped cross-section.
 14. The frame of claim 13wherein the I-shaped cross-section is locally ribbed in a horizontalsection passing through a mid-plane of the I-shaped cross-section. 15.The frame of claim 13 wherein the I-shaped cross-section is variable andis curved toward the blade.